The present Applicant has already proposed a disk recording apparatus according to which the information is recorded in a data format standardized in a compact disk (CD), using a recordable disk, such as a magneto-optical disk, having a vertical magnetization film exhibiting magneto-optical effect as the magnetic recording layer, as shown for example in PCT/JP87/00764.
Referring to a diagrammatic view of FIG. 1, a pre-recorded region 5 in which a circumferentially extending pattern of projections and recesses is previously formed by pits 4 and a data recording region 6 in which the magneto-optical recording is performed are arranged alternately each at an equal pitch in each land region 3 defined between spirally extending pre-grooves 2 on a magneto-optical disk 1 used as the recording medium in the above disk recording apparatus.
In the data format, standardized in the compact disk (CD), information data of each processing unit or frame are formed by 33 symbols (264 bits) made up of 24 symbols (12 words) each composed of eight bits, each four symbols of error correction codes P and Q and a symbol as a sub-code for control or user data. The data bit of each frame is subjected to a so-called eight to fourteen modulation (EFM) so that the eight bit data of each symbol are converted into a 14-bit pattern to produce 14.times.33 bits or 33 symbols, to which 24-bit sync signals are annexed. Three merging bits each are placed between adjacent symbols to produce 588 channel bits which make up one frame shown in FIG. 2. The eight bits of the one symbol annexed as the aforementioned control data or user data from sub-code channels P, Q, R, S, T, U, V and W constitute a data block or a large frame composed of 98 symbols corresponding to 98 frames, as shown in FIG. 3. Meanwhile, the two symbols at the leading part of the block are dedicated to sync patterns S0 and S1 for demarcating the boundary of this data block.
In the above described magneto-optical disk 1, the frame sync signals and the sub-code among the 588 channel bits making up each frame are recorded in advance as a pattern of projections and recesses on the pre-recorded region 5 by molding and the absolute time or absolute address information from the start position of the data record region 6 is afforded by the Q-channel of the aforementioned sub-code.
In the above described disk recording apparatus, making use of the magneto-optical disk 1, data such as play information and parity are photomagnetically recorded on the data record region 6, while the disk rotation control is performed at a CLV or constant linear velocity on the basis of the reproducing output from the pre-recorded region 5 of the disk 1 and tracking servo as well as focusing servo is applied to the optical head.
In the above described disk recording apparatus, when the servo for the optical head is disturbed by some perturbation or malfunction such as vibration or noises in the power source to give rise to abnormal conditions such as incorrect focussing servo control or track jumps, interrupted portions are produced in the data recorded on the magneto-optical disk at the time point of occurrence of these abnormal conditions.
The present Applicant has already proposed a disk recording apparatus wherein the track jump is detected during the recording operation and, on occurrence of a track jump, the laser power of the optical head is lowered to the reproducing level, and then the optical head is controlled to jump tracks to the desired track and operation is resumed on the desired track to prevent the information from being recorded in other than the desired track, as shown for example in PCT/JP88/00196.
Meanwhile, if such interruption of the record data should occur during the time the disk recording apparatus is used as the computer terminal, it is possible to re-read the record data by the communication exchange procedure with the host computer to make re-recording from the leading end of the interrupted portion.
It is possible in this manner to lower the laser power of the optical head to the reproducing level, and to perform the track jump control to cause the recording operation to be resumed at the desired track to prevent the information from being erroneously recorded in other than the desired track. However, when recording continuous data on a real time basis, as in live recording of musical performance, the interrupted portion cannot actually be recovered. Even supposing that the optical head is returned immediately to the original recording track, the musical performance data is lost for the time interval that has elapsed during control of the track jump. Thus there is necessarily the risk that the listener cannot but feel disagreeable on account of occurrence of the interrupted portion during the musical performance at the time of reproduction.
The present invention has been made in view of the foregoing and is aimed to provide a disk recording apparatus wherein, even when abnormal conditions such as incorrect focussing servo or track jump should occur in the optical head during data recording, record data loss may be avoided in advance to permit data to be recorded correctly.